8 INTRODUCTION. 



An object is examined by " direct " light when it is 

 examined by the light which falls upon its surface with- 

 out passing through it. This is the common method 

 with the hand lens. 



An object is examined by " transmitted " light when 

 the light passes through it before entering the eye. 

 This is the common method with the compound mi- 

 croscope. Ordinarily, when transmitted light is used, 

 direct light should be cut off as far as possible. 



An object is examined by " oblique " light when the 

 light passes through it so obliquely that only that re- 

 fracted by the object enters the eye. It therefore ap- 

 pears light against a dark ground. 



IV. SECTION CUTTING. 



Sections. A section is a very thin slice taken from the 

 interior of any organ. It should be of as nearly equal 

 thickness in all parts as possible. The term " slice " is 

 used to designate a thin piece cut from the surface of 

 any organ. 



By a transverse section is meant one at right angles 

 to the long axis of the object. Unless care is exercised 

 the surface from which the sections are being cut will 

 become inclined. Especially is this likely when the 

 object is large or is supported in pith. The pith stick 

 should be trimmed down at the end so as to leave only 

 enough to support the object. The chief cause of the 

 tendency to become inclined is that the under side of 

 the razor is not flat ; hence the larger the object, the 

 more likely the transverse sections are not to be truly 

 transverse. 



By a longitudinal section is meant one which is 



